Page 49 - 《橡塑技术与装备》英文版2025年12月

MATERIALS AND FORMULATIONS

divided into components A and B. Components A and B are approximately 25~45 um, and after heating, the volume rapidly
mixed and supplied in a 1:1 ratio, and both components have expands to several dozen times its original size, thus achieving
essentially the same viscosity and density. The catalyst is a the foaming effect. The microsphere foaming can withstand
platinum-based catalyst. The performance indicators of the temperatures up to 180°. The typical filling amount is 1%~5%.
selected addition-type liquid silicone are shown in Table 1. (2) Sodium bicarbonate: Selecting sodium bicarbonate
Table 1 Properties of addition-type liquid silicone that has undergone surface treatment can improve the foaming
rubber effect.
Viscosity Relative Density (25 ℃) Hardness/ Tensile Strength
.
.
-3
/(Pa S) /(g cm ) (ShoreA) / MPa (3) Hollow glass microspheres: Hollow glass
3 500 1.09 50 10.0 microspheres are a kind of micron-sized hollow glass
microspheres with a smooth surface. Their main chemical
Organic compounds containing N, P, and S can poison
composition is soda-lime borosilicate glass, and they appear as
platinum catalysts, leading to poor sulfiding and inhibiting hollow transparent spheres under a microscope. Hollow glass
the reaction. Therefore, the foaming agent should be selected
microspheres possess various properties such as low density,
without the aforementioned elements. Currently, three foaming
high strength, low thermal conductivity, electrical insulation,
agents are being used, as follows:
high temperature resistance, acid and alkali resistance, good
(1) A kind of physical foaming agent: It has a core-
fluidity, and chemical stability. The performance indicators of
shell structure, with the outer shell being a thermoplastic
this type of hollow glass microspheres are shown in Table 2,
acrylic resin polymer and the inner core being spherical
and the typical addition amount is 5% to 8%.
plastic particles composed of alkane gases. The diameter is
Table 2 Performance indicators of hollow glass microspheres
Serial Number Detection Content Unit Control Indicator Test Results
1 Exterior color - white white
2 Humidity % ≤ 0.50 0.2
3 Floatation rate % ≥ 95 98
4 bulk density g/cm3 0.19~0.22 0.2
5 particle size μm D90 ≤ 65 63.86
6 true density g/cm 3 0.37~0.39 0.386 5
7 Compressive strength (crushing rate) % 5500psi qualified

1.2 Sample preparation filling ratio specified in Table 4 and mix them evenly. Use a flat
Add the physical foaming agent to the addition-type curing press to press the mixture into sheets to obtain foaming
liquid silicone rubber according to the filling ratio in Table materials. The process parameters are shown in Table 4, and no
3 and mix them evenly. Use a flat curing press to press the pressure is applied during curing. After molding, use a cutter to
mixture into sheets to obtain foaming materials, with the cut the test pieces into standard samples.
process parameters shown in Table 3. After molding, cut the Table 4 Experimental formula and process parameters
test pieces into standard samples with a cutting knife. using sodium bicarbonate as a foaming aid
Serial Fill and Add Process Curing Time
Table 3 Experimental formula and process parameters Number Proportion Temperature / ℃ (in minutes)
using physical foaming agent T1 0.5% 130 10
Serial Fill and Add Process Curing Time Molding T2 2% 130 10
number proportion temperature/ ℃ (in minutes) Pressure / MPa T3 3% 130 10
W1 1% 120 10 15
W2 1% 120 10 none
W3 2% 120 10 15 Add hollow glass microspheres into the addition-type
W4 2% 120 10 none liquid silicone rubber according to the filling ratio specified in
W5 4% 120 10 15
W6 4% 120 10 none Table 5 and mix them evenly. Use a flat curing press to press
the mixture into sheets to obtain foamed materials. The process
Add the surface-treated foaming aid, sodium bicarbonate, parameters are shown in Table 5, and no pressure is applied
to the addition-type liquid silicone rubber according to the during curing. After molding, use a cutting knife to cut the test

Vol.51，2025 ·43·